Cellulose Technology Research

11 Formation and Properties of Blended Nonwovens Produced by Cellulose-Cellulose Bonding R A Y M O N D A. Y O U N G and B E R N A R D M I L L E R

Downloaded by UNIV LAVAL on July 11, 2016 | http://pubs.acs.org Publication Date: June 1, 1975 | doi: 10.1021/bk-1975-0010.ch011

Textile Research Institute, Princeton, N.J. 08540

Abstract A s e r i e s o f s e l f - b o n d e d nonwoven fabrics have been produced from cellulosic fibers and from cellulose fiber/noncellulose ( n a t u r a l o r manmade) f i b e r b l e n d s by treatment of cross-laid c a r d webs w i t h c o n c e n t r a ted zinc chloride s o l u t i o n s . The cellulosic fibers become c o h e s i v e l y bonded d u r i n g the t r e a t m e n t . If noncellulosic f i b e r s have been blended in d u r i n g the c a r d i n g o p e r a t i o n , t h e i r mechanical entanglement will be enhanced by this b o n d i n g . A number o f parameters, such as z i n c c h l o r i d e c o n c e n t r a t i o n , can be v a r i e d to produce a range o f d e s i r e d p h y s i c a l p r o p e r t i e s and aesthetic characteristics. U s e f u l n e s s of these n o n wovens in filtration s t u d i e s has been demonstrated. Introduction Nonwoven f a b r i c s are b e i n g used on an i n c r e a s i n g s c a l e and i n a w i d e n i n g v a r i e t y o f a p p l i c a t i o n s (1,2). G e n e r a l l y , the manufacture o f t h e s e m a t e r i a l s i n v o l v e s f o r m a t i o n o f a f i b r o u s network or web, r e i n f o r c e m e n t o f t h e web, and f i n i s h i n g o f the p r o d u c t . The many methods f o r a c c o m p l i s h i n g t h i s sequence may be c l a s s i f i e d on the b a s i s o f whether the web i s w e t l a i d or d r y - l a i d . In the wet p r o c e s s the f i b e r s a r e suspended i n water and p r o c e s s e d e s s e n t i a l l y as i n papermaking, whereas i n the d r y p r o c e s s the f i b r o u s web i s produced i n the d r y s t a t e e i t h e r by c a r d i n g o r u s i n g s p e c i a l aerodynamic equipment d e s i g n e d t o g i v e an i s o t r o p i c web. One o f t h r e e b a s i c methods i s u s u a l l y employed t o a c h i e v e bonding i n d r y - l a i d webs: mechanical entanglement, a d h e s i v e b i n d i n g , o r f i b e r f u s i o n . To o b t a i n s t r e n g t h t h r o u g h m e c h a n i c a l entanglement 160

Turbak; Cellulose Technology Research ACS Symposium Series; American Chemical Society: Washington, DC, 1975.


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a l o n e , n e e d l e p u n c h i n g methods a r e most o f t e n u s e d . A d h e s i v e b i n d i n g r e q u i r e s the a d d i t i o n o f a n o t h e r substance t o cement or b i n d f i b e r s a t c r o s s o v e r points. P o l y m e r i c b i n d i n g agents used have i n c l u d e d a c r y l i c s , polyvinyl chloride, polyvinyl acetate, c e l l u l o s e e s t e r s , and p o l y u r e t h a n e s . To a c o n s i d e r a b l e e x t e n t , the c h a r a c t e r i s t i c s o f t h e f i n a l p r o d u c t depend on the f i b e r - b i n d e r r a t i o (2). A growing number o f f i b e r f u s i o n t e c h n i q u e s are becoming i n c r e a s i n g l y i m p o r t a n t i n the p r o d u c t i o n o f nonwovens. Spunbonded f a b r i c s , f o r example, are produced d i r e c t l y from e x t r u d e d polymer s t o c k . The e x t r u d e d f i l a m e n t s are charged e l e c t r o s t a t i c a l l y so t h a t t h e y b a l l o o n , c o l l e c t e d on a moving c o n v e y e r , and then t h e r m a l l y -bonded ( 2 , 3 ) . In o t h e r t h e r m a l f u s i o n p r o c e s s e s , f i b e r s o f a t h e r m o p l a s t i c polymer a r e used as one component o f t h e web, and b o n d i n g i s a c h i e v e d by h e a t i n g or c a l e n d e r i n g a t the a p p r o p r i ate t e m p e r a t u r e ( 4 ) . S o l v e n t f u s i o n r e q u i r e s h e a t i n g the web i n the p r e s e n c e o f a s o l v e n t t h a t i n t e r a c t s w i t h a web component (5). A n o t h e r method o f f i b e r f u s i o n i s t h e autogeneous b o n d i n g o f n y l o n f i b e r s by t r e a t m e n t w i t h gaseous h y d r o c h l o r i c a c i d (6). T h i s t r e a t m e n t a p p a r e n t l y causes s u r f a c e d e c r y s t a l l i z a t i o n and p l a s t i c i z a t i o n o f the n y l o n f i b e r s and subsequent b o n d i n g upon r e m o v a l o f the a c i d i c g a s . The t e c h n i q u e , however, i s s p e c i f i c t o n y l o n f i b e r s and s u f f e r s the a d d i t i o n a l d i s a d v a n t a g e t h a t many o t h e r f i b e r s cannot be used i n b l e n d s w i t h the n y l o n because o f p o s s i b l e d e g r a d a t i o n d u r i n g the gaseous HC1 t r e a t m e n t . The method d e s c r i b e d i n t h i s r e p o r t f o r p r o d u c t i o n o f nonwoven f a b r i c s can be c l a s s i f i e d as a f i b e r fusion technique. In t h i s c a s e , c e l l u l o s i c f i b e r s are p a r t i a l l y d e c r y s t a l l i z e d and s o l u b i l i z e d by a c o n c e n t r a t e d aqueous s o l u t i o n o f z i n c c h l o r i d e and are bonded on removal o f t h e s a l t s o l u t i o n . In t h i s way i t i s p o s s i b l e t o bond c o t t o n o r r a y o n webs w i t h o u t the use o f a d h e s i v e b i n d e r s which f r e q u e n t l y m o d i f y p h y s i c a l p r o p e r t i e s and which may a l t e r s i g n i f i c a n t l y the c h e m i c a l c h a r a c t e r i s t i c s o f the material (e.g., i t s flammability behavior). In a d d i t i o n , t h i s method a v o i d s the d e t r i m e n t a l e f f e c t s o f h i g h t e m p e r a t u r e s or c h e m i c a l r e a g e n t s which a r e normally necessary f o r fusion bonding. Consequently, t h i s b o n d i n g method can be used b o t h w i t h t o t a l l y c e l l u l o s i c f i b e r systems and w i t h most c e l l u l o s i c / n o n c e l l u l o s i c ( n a t u r a l or manmade) f i b e r blends. Z i n c c h l o r i d e t r e a t m e n t s have l o n g been used f o r



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bonding m u l t i p l i e s of c e l l u l o s e sheets, r e s u l t i n g i n r i g i d i n d u s t r i a l m a t e r i a l s whose p h y s i c a l p r o p e r t i e s resemble p l a s t i c l a m i n a t e s made from r e s i n - p a p e r systems ( 7 , 8 ) » The use o f c o n c e n t r a t e d aqueous z i n c c h l o r i d e s o l u t i o n s as an a f t e r t r e a t m e n t f o r enhance ment o f s t r e n g t h p r o p e r t i e s o f p r e v i o u s l y bonded r a y o n nonwoven f a b r i c s has a l s o been d e s c r i b e d (9). F i g u r e 1, taken from the work o f P a t i l e t a l . (10), d e p i c t s the e f f e c t o f z i n c c h l o r i d e s o l u t i o n s on the c r y s t a l l i n i t y o f c o t t o n c e l l u l o s e as measured by x-ray fiber d i f f r a c t i o n . Depending on the c o n d i t i o n s o f t r e a t m e n t , z i n c c h l o r i d e s o l u t i o n s can cause a l m o s t t o t a l de c r y s t a l l i z a t i o n o f a c e l l u l o s e sample. The s t r e n g t h o f a nonwoven web o f c e l l u l o s i c f i b e r s treated with a concentrated s o l u t i o n of zinc c h l o r i d e and t h e n washed would presumably r e s u l t from i n t e r f i b e r b o n d i n g accompanying r e c r y s t a l l i z a t i o n o f t h e s o l u b i l i z e d c e l l u l o s e upon removal o f the z i n c c h l o r i d e . T h i s r e p o r t summarizes r e c e n t s t u d i e s on t h e use o f such t r e a t m e n t t o produce n o n woven f a b r i c s from c r o s s - l a i d webs o f c e l l u l o s e and cellulose/manmade f i b e r b l e n d s . Experimental M a t e r i a l s and Methods. Manmade f i b e r s . A l l the manmade f i b e r s used i n t h i s s t u d y were c r i m p e d and had the f o l l o w i n g s p e c i f i c a t i o n s : rayon - 5.5 d e n i e r , 1 - 1 / 1 6 - i n . staple l e n g t h (FMC C o r p . ) ; p o l y e s t e r - 4.5 d e n i e r , 1 - 9 / 1 6 - i n . s t a p l e l e n g t h ( Ε . I . du Pont de Nemours & C o . , I n c . ) ; n y l o n - 3 d e n i e r , 1 - 1 / 2 - i n . s t a p l e l e n g t h ( Ε . I . du Pont de Nemours & C o . , I n c . ) ; a c r y l i c - 2 d e n i e r , 2 - i n . s t a p l e l e n g t h (Dow B a d i s c h e C o . ) . C o t t o n . A c a l a c o t t o n c a r d s l i v e r was s c o u r e d w i t h b o i l i n g 5% sodium h y d r o x i d e under r e f l u x f o r 4 h r , washed t h o r o u g h l y w i t h w a t e r , and a i r d r i e d . The a i r - d r i e d f i b e r s were formed i n t o c a r d webs w i t h o u t further treatment. Zinc c h l o r i d e . Standard s o l u t i o n s o f z i n c c h l o r i d e were p r e p a r e d by u s i n g the F i s h e r t e c h n i c a l grade c h e m i c a l . The c o n c e n t r a t i o n o f the s o l u t i o n s was d e t e r m i n e d t h r o u g h measurements o f s p e c i f i c g r a v i t i e s by w e i g h i n g 25-ml o f the s o l u t i o n t o the n e a r e s t 0 . 1 mg i n a s e a l e d , 25-ml v o l u m e t r i c f l a s k . The c o n c e n t r a t i o n o f the s o l u t i o n was then o b t a i n e d from a t a b l e o f s p e c i f i c g r a v i t y v e r s u s c o n c e n t r a -


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F o r m a t i o n o f Nonwoven M a t s . The f i b e r s were f i r s t formed i n t o a 1 5 - i n . wide c a r d web and c u t i n t o f o u r equal sections. ( I f more than one type o f f i b e r was t o be i n c l u d e d i n the mat, t h e b l e n d i n g o f the f i b e r s was done d u r i n g t h e c a r d i n g o p e r a t i o n . ) The f o u r s e c t i o n s were c r o s s - l a i d a l t e r n a t i n g the c a r d i n g d i r e c t i o n i n each l a y e r . S i x - i n c h squares o f t h i s mat were s a t u r a t e d w i t h c o n c e n t r a t e d aqueous z i n c c h l o r i d e , passed t h r o u g h a p r e s s u r e n i p t o remove e x c e s s s o l u t i o n , and p l a c e d i n a C a r v e r p r e s s between T e f l o n " s h e e t s . The mats were t h e n p r e s s e d a t 2 p s i f o r one min a t 1 0 0 ° C . Immediately a f t e r removal from the p r e s s , the z i n c c h l o r i d e was l e a c h e d from the f a b r i c i n a r u n n i n g water b a t h . The e x c e s s water was then p r e s s e d out and the mat d r i e d i n the Carver press at 100°C at β p s i . The f i n a l t h i c k n e s s and d e n s i t y c o u l d be a d j u s t e d t o some e x t e n t d u r i n g the f i n a l p r e s s i n g . R e s u l t s and D i s c u s s i o n S t r e n g t h P r o p e r t i e s . The e a r l i e r work o f P a t i l e t a l . (10) ( F i g . 1) demonstrated the c r i t i c a l range of concentration necessary f o r d e c r y s t a l l i z a t i o n of cotton c e l l u l o s e . T h i s c o n c e n t r a t i o n dependence p r o b a b l y i s the r e s u l t o f the marked e f f e c t o f i o n i c d i s t r i b u t i o n on the assumed z i n c c h l o r i d e c e l l u l o s e complex (12). The z i n c c h l o r i d e s o l u t i o n has e s s e n t i a l l y no e f f e c t on t h e c e l l u l o s e c r y s t a l s t r u c t u r e e i t h e r below a c o n c e n t r a t i o n o f 60% (W/W) o r above 75%. The c u r v e s i n F i g u r e 1 a l s o i n d i c a t e t h a t cotton d e c r y s t a l l i z a t i o n i s extremely s e n s i t i v e t o r e l a t i v e l y s m a l l changes i n t e m p e r a t u r e . F i g u r e 2 d e p i c t s t e n s i l e s t r e n g t h as a f u n c t i o n o f z i n c c h l o r i d e c o n c e n t r a t i o n f o r a s e r i e s of c a r d e d c o t t o n webs bonded a c c o r d i n g t o the p r o c e d u r e d e s c r i b e d i n the p r e v i o u s s e c t i o n . The e f f e c t o f z i n c c h l o r i d e c o n c e n t r a t i o n on t h e t e n s i l e s t r e n g t h o f the c o t t o n nonwovens c l o s e l y p a r a l l e l s the r e p o r t e d e f f e c t on the e x t e n t o f d e c r y s t a l l i z a t i o n o f cotton (Fig. 1). The maximum s t r e n g t h was a c h i e v e d a t about 72-73% z i n c c h l o r i d e ( F i g . 2 ) , the same range o b s e r v e d f o r maximum d e c r y s t a l l i z a t i o n . F i g u r e 3 shows the t e n s i l e s t r e n g t h s o f a 100% rayon sample and o f a r a y o n / p o l y e s t e r (75/25) b l e n d a f une t i on o f z i n c c h l o r i d e c o n c e n t r a t i o n . The maximum s t r e n g t h s o f b o t h r a y o n - b a s e d nonwovens a r e




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Figure 1.

Decrystallization of cotton by zinc chloride

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ZnCl CONC.,% 2

Figure 2. Tensile strength of zinc chloride-bonded scoured cotton nonwovens as a function of zinc chloride concentration



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about h a l f t h a t o f the c o t t o n nonwoven. These strength d i f f e r e n c e s probably r e f l e c t differences i n f i b e r s t r e n g t h , the c o t t o n h a v i n g 1.5 t o 2 times the t e n a c i t y o f the r a y o n f i b e r (13). In a d d i t i o n , i t appears t h a t a much lower c o n c e n t r a t i o n o f z i n c c h l o r i d e , about 56%, i s n e c e s s a r y f o r o b t a i n i n g maximum s t r e n g t h w i t h r a y o n - b a s e d s y s t e m s . This d i f f e r e n c e i s most l i k e l y a r e f l e c t i o n o f d i f f e r e n c e s i n t h e c r y s t a l l i n e c h a r a c t e r o f t h e two t y p e s of cellulose fibers. Rayon has a c r y s t a l l i n i t y of about 40% and c o t t o n c l o s e t o 70% as d e t e r m i n e d by x - r a y f i b e r d i f f r a c t i o n (14). F u r t h e r m o r e , rayon has a c e l l u l o s e II c r y s t a l l i n e l a t t i c e s t r u c t u r e , w h i l e c o t t o n has the n a t i v e c e l l u l o s e I c r y s t a l l i n e lattice structure. A t v e r y h i g h c o n c e n t r a t i o n s o f z i n c c h l o r i d e , the rayon was found t o form a weak g e l - l i k e f i l m under the bonding c o n d i t i o n s used i n t h i s study ( F i g . 3 ) . F i l m f o r m a t i o n under t h e s e c o n d i t i o n s i s t h e r e s u l t o f t o t a l d e c r y s t a l l i z a t i o n and l o s s o f rayon f i b e r structure. T h i s i l l u s t r a t e s the p r i n c i p l e t h a t i n o r d e r t o a c h i e v e t e x t i l e - l i k e nonwovens o f a c c e p t a b l e s t r e n g t h , b u l k d e c r y s t a l l i z a t i o n i s t o be a v o i d e d and f i b e r s t r u c t u r e must be m a i n t a i n e d . T h u s , the z i n c c h l o r i d e t r e a t m e n t must i n d u c e o n l y s u r f a c e d e c r y s t a l l i z a t i o n o f the c e l l u l o s i c f i b e r s . The s t r e n g t h of the nonwoven can then be maximized through an optimum c o m b i n a t i o n o f e x t e n t o f bonding and m e c h a n i c a l e n t a n g l e m e n t . With t h e b l e n d e d systems, the s t r e n g t h of t h e nonwoven mat r e s u l t s from b o t h bonding and m e c h a n i c a l entanglement o f the c e l l u l o s i c f i b e r , and from p u r e l y m e c h a n i c a l entanglement o f the n o n c e l l u l o s i c f i b e r component. The h i g h e r s t r e n g t h o f the r a y o n / p o l y e s t e r b l e n d ( F i g . 3) r e f l e c t s the h i g h e r s t r e n g t h o f t h e m e c h a n i c a l l y e n t a n g l e d p o l y e s t e r component. The t e n s i l e s t r e n g t h s of two o t h e r b l e n d e d systems, r a y o n / n y l o n and r a y o n / a c r y l i c , as a f u n c t i o n o f the rayon c o n t e n t i n the b l e n d a r e shown i n F i g u r e 4. I t was e x p e c t e d t h a t as the amount o f rayon i n t h e b l e n d i n c r e a s e d , the t e n s i l e s t r e n g t h would a l s o p r o g r e s s i v e l y i n c r e a s e . T h i s tendency was o b s e r v e d f o r the r a y o n / n y l o n b l e n d ( F i g . 4 ) , where t h e s t r e n g t h of t h e b l e n d i n c r e a s e d f o r a b l e n d c o n t a i n i n g 60% rayon t o 0.9 g / t e x , the same s t r e n g t h measured f o r t h e 10 0% rayon system. It is l i k e l y t h a t a maximum t e n s i l e s t r e n g t h f o r r a y o n / n y l o n o c c u r s somewhere between 60 and 100% rayon. T h i s would be c o n s i s t e n t w i t h the r e s u l t s shown i n F i g u r e 3 f o r r a y o n / p o l y e s t e r . The



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Figure 3.

Tensile strength of zinc chloride-bonded nonwovens as a function of zinc chloride concentration

Figure 4. Tensile strength of zinc chloride-bonded nonwovens as a function of rayon content in the blend



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r a y o n / a c r y l i c b l e n d , however, behaved i n a d i f f e r e n t manner. I n s t e a d o f showing enhanced t e n s i l e strength w i t h i n c r e a s i n g amounts o f r a y o n i n t h e b l e n d , t h i s system showed an o p p o s i t e c o r r e l a t i o n . T h i s was most l i k e l y caused by i n t e r a c t i o n o f the a c r y l i c f i b e r w i t h the z i n c c h l o r i d e s o l u t i o n , s i n c e t h e s e s o l u t i o n s are a t l e a s t p a r t i a l solvents f o r p o l y a c r y l o n i t r i l e polymers. Under t h e b o n d i n g c o n d i t i o n s used i n t h e s e e x p e r i m e n t s , i t was found t h a t w i t h a 100% a c r y l i c mat a f i l m y m a t e r i a l was formed a f t e r zinc chloride treatments. This a c r y l i c f i l m i n c o m b i n a t i o n w i t h s m a l l amounts o f rayon formed a s t r o n g u n i f o r m mat. However, a t lower l e v e l s o f a c r y l i c f i b e r i n t h e b l e n d , the a c r y l i c f i l m e x h i b i t e d n o n u n i f o r m s h r i n k a g e c r e a t i n g gaps i n the nonwoven s t r u c t u r e which reduced the s t r e n g t h properties. The p o s s i b l e u t i l i z a t i o n o f t h e i n t e r a c t i o n o f a c r y l i c f i b e r s w i t h c o n c e n t r a t e d aqueous s o l u t i o n s o f z i n c c h l o r i d e f o r b o n d i n g o f nonwoven webs i s under f u r t h e r i n v e s t i g a t i o n . Electron Microscopy. F i g u r e s 5 and 6 show s c a n n i n g e l e c t r o n m i c r o g r a p h s o f s e c t i o n s o f a rayon nonwoven mat bonded w i t h 56% z i n c c h l o r i d e under t h e standard c o n d i t i o n s . S e v e r a l f i b e r c r o s s i n g s are shown i n F i g u r e 5A (300X) w i t h one o f t h e s e e x h i b i t i n g apparent bonding between t h e f i b e r s . The o c c a s i o n a l b o n d i n g which e x i s t s i n t h e s e s t r u c t u r e s i s m a i n l y r e s p o n s i b l e f o r the f l e x i b i l i t y needed i n the nonwoven system, s i n c e e x c e s s i v e b o n d i n g g i v e s a s t i f f board-like material. Under h i g h e r m a g n i f i c a t i o n (100OX) the n a t u r e o f t h e bonded a r e a i s c l a r i f i e d ( F i g . 5B). Though t h e f i b e r s t r u c t u r e appears i n t a c t , t h e r e has been e x t e n s i v e s u r f a c e d e c r y s t a l l i z a t i o n and s o l u b i l i z a t i o n c a u s i n g a m e l d i n g o f t h e f i b e r s by a c e l l u l o s e - c e l l u l o s e bond, which forms a f t e r l e a c h i n g removes t h e z i n c c h l o r i d e . F i g u r e 6 shows e l e c t r o n m i c r o g r a p h s o f a d e l a m i n a t e d z i n c c h l o r i d e - b o n d e d rayon nonwoven. F i g u r e 6A (300X) d e p i c t s a l o c a t i o n where a p p a r e n t l y t h e r e has been f i b e r - f i b e r p u l l o u t a t a bonded p o i n t as a r e s u l t o f t h e d e l a m i n a t i o n . A l s o shown a r e f i b e r s where no bonds were formed b u t which add s t r e n g t h t h r o u g h m e c h a n i c a l entanglement. A t higher m a g n i f i c a t i o n (1000X) t h e f i l m y c h a r a c t e r o f t h e broken bond becomes e v i d e n t . The d e c r y s t a l l i z a t i o n and s o l u b i l i z a t i o n i s a p p a r e n t l y l o c a l i z e d t o some e x t e n t a t f i b e r - f i b e r c r o s s i n g s , s i n c e t h e remainder o f t h e f i b e r shows o n l y l e s s e r e f f e c t s o f the z i n c c h l o r i d e treatment (also c f · F i g . 5A).




Figure 5. Scanning electron micrographs of sections of a zinc chloride-bonded rayon nonwoven (A—128X, B—425X)

Figure 6. Scanning electron micrographs of a delaminated zinc chloride-bonded rayon nonwoven (A—128X, Β—425X)



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Air Particulate F i l t r a t i o n . One o f t h e many a p p l i c a t i o n s f o r nonwoven f a b r i c s i s t h e i r u s e as a i r filters. A s e r i e s o f p r e l i m i n a r y experiments u s i n g the c e l l u l o s e - b a s e d , z i n c c h l o r i d e - b o n d e d f a b r i c s as f i l t e r media have been conducted i n t h e f i l t r a t i o n l a b o r a t o r y a t TRI ( 1 5 ) . F i g u r e 7 shows f i l t r a t i o n e f f i c i e n c i e s as a f u n c t i o n o f mat d e n s i t y f o r s e v e r a l of the zinc chloride-bonded f a b r i c s . A t very high d e n s i t i e s a l l t h e f a b r i c s g i v e e s s e n t i a l l y t h e same h i g h e f f i c i e n c y ; however, t h i s i s t r i v i a l , s i n c e the e x c e s s i v e d r a g and t h e r e s u l t a n t energy consumption would be u n a c c e p t a b l e . In terms o f f i l t r a t i o n p e r formance, i t i s n e c e s s a r y t o d e v e l o p f i l t e r s t h a t g i v e h i g h e f f i c i e n c y w i t h m i n i m a l d r a g ( i . e . , low density). D i s t i n c t d i f f e r e n c e s a r e n o t e d among t h e d i f f e r e n t f i b e r t y p e s w i t h f a b r i c s o f lower d e n s i ties. Cotton maintains the highest e f f i c i e n c y at a l l d e n s i t y l e v e l s , which i s p r o b a b l y due t o t h e much lower l i n e a r d e n s i t y o f t h e c o t t o n f i b e r as compared t o t h a t o f the r a y o n (5.5 d e n i e r ) and p o l y e s t e r (4.5 d e n i e r ) f i b e r s . T h u s , w i t h t h e c o t t o n mat a t a g i v e n d e n s i t y o r w e i g h t t h e r e a r e many more f i b e r s r e s u l t i n g i n many more f i b e r c r o s s i n g s and c h a n n e l s per u n i t area to give g r e a t e r e f f i c i e n c y . On t h e o t h e r h a n d , t h e r a y o n and p o l y e s t e r f i b e r s have about t h e same d i m e n s i o n s . The h i g h e r e f f i c i e n c y o f the r a y o n / p o l y e s t e r b l e n d as compared t o t h a t o f t h e a l l rayon must, t h e r e f o r e , be i n p a r t r e l a t e d t o t h e d i f f e r e n t surface c h a r a c t e r i s t i c s of the polyester component which a p p a r e n t l y enhances f i l t r a t i o n p e r formance. S t u d i e s o f t h e use o f o t h e r b l e n d e d f i b e r systems f o r f i l t r L a t i o n a p p l i c a t i o n s are i n p r o g r e s s . Literature Cited 1. C a r t e r , H . J . , T a p p i , (1974), 57, 50. 2. R o s s , S. E., Chem. T e c h . , (1972), 2, 535. 3. E r i c s o n , C . E . , " B o n d i n g in Spunbonded Non wovens", Textile Research I n s t i t u t e Seminar, O c t o b e r 21, 1974. 4. W i n c h e s t e r , S . C . and W h i t w e l l , J . C . , T e x t i l e R e s . J., (1970), 40, 458-471. 5. T e c h n i c a l B u l l e t i n , " P r o d u c t i o n o f Nonwoven F a b r i c s " , B a d i s c h e Anilin and S o d a - F a b r i k A G , (BASF). 6. M a l l o n e e , W. C . and H a r r i s , Η . E., Gas Activated Bonding o f N y l o n s , U . S . P a t e n t 3,516,900 (June 23, 1970).




170

Figure 7. Filtration efficiency of zinc chloride-bonded nonwovens as a function of mat density


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7. 8. 9. 10. 11. 12.


13. 14.

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AND MILLER

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T a y l o r , T . , B r i t . P a t . 787 (March 29, 1859); U . S . P a t . 114, 830 (March 16, 1871). L e e , L . T . C . , T a p p i , (1964), 47, 386. T e c h . S e r . Bull., S-12R, American V i s c o s e Div., FMC Corp., Marcus Hook, P a . , J u l y 15, 1968. Patil, Ν. B . , D w e l t z , Ν. E., and R a d h a k r i s h n a n , T . , T e x t i l e R e s . J., (1965), 35, 517. I n t e r n a t i o n a l C r i t i c a l T a b l e s , 1 s t ed., Vol. III, M c G r a w - H i l l , New Y o r k , 1928, p . 64. R i c h a r d , N . J. and W i l l i a m s , D . G . , C a r b o h y d . R e s . (1970), 12, 409. M o r t o n , W. E. and H e a r l e , J. W. S . , " P h y s i c a l P r o p e r t i e s o f T e x t i l e F i b e r s " , p . 285, B u t t e r w o r t h Ltd., London, 1962. O t t , E . , Spurlin, Α. Μ . , and Grafflin, M. W . , e d s . , C e l l u l o s e and C e l l u l o s e D e r i v a t i v e s , P a r t I , New Y o r k , I n t e r s c i e n c e P u b . , 1954, p . 273. M i l l e r , B., Lamb, G . E . R . , and C o s t a n z a , P., "Nonwovens, A Study o f C r i t i c a l F i b e r Vari ables", Tappi, i n press.


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